1. Field of Invention
The present invention relates to a method of reducing nitrogen oxide using an amine compound as a reductant.
2. Description of Related Art
Around the globe, development of environmentally-friendly vehicle engines exhausting CO2 in a small amount and having excellent energy efficiency has attracted attention due to global warming and high oil prices. A currently developed diesel engine is a high fuel-efficient engine, and exhausts CO2 in a small amount, and thus research and development thereof have been actively conducted in Europe and Korea.
However, the diesel engine has a problem in that even though the exhaust amount of CO2 is small, nitrogen oxide (NOx) and particulate materials (PM), which are harmful to a human body and the environment, are exhausted. Particularly, since nitrogen oxide is a main cause material of smogs and acid rains and regulation thereof has gradually been reinforced in advanced countries and Korea, nitrogen oxide should be essentially removed through an exhaust gas post-treatment system. As described above, in accordance with gradual reinforcement of regulation of nitrogen oxide, development of an exhaust gas post-treatment technology is further required together with improvement in engine.
In the diesel engine, a temperature of an exhaust gas of a light-duty vehicle is 150° C. to 250° C. and a temperature of a heavy-duty vehicle is about 200° C. to 350° C., and the temperature of the exhaust gas is slightly low (R. G. Gonzales, “Diesel Exhaust Emission System Temperature Test”, T&D Report 0851-1816P, SDTDC, U.S. Department of Agriculture, December 2008). Accordingly, the exhaust gas post-treatment technology of the diesel engine requires a catalyst system that can remove nitrogen oxide even at low temperatures.
Currently, in order to overcome tightened regulation of the exhaust gas at home and abroad, a urea selective catalytic reduction (SCR) technology and a NOx adsorber technology (lean NOx trap, LNT) have been developed as a method of efficiently removing nitrogen oxide exhausted from the diesel engine. The urea/SCR technology is a technology of removing nitrogen oxide by using urea as a reductant and zeolite as a catalyst to selectively reduce nitrogen oxide, and is known as a technology having the most excellent performance at low temperatures among currently developed technologies of removing nitrogen oxide. However, the urea/SCR technology has technical inferiorities in that hydrothermal stability is low and a catalyst activity easily deteriorates by SO2 and hydrocarbons included in the exhaust gas, and also has problems in that a urea storage device should be further installed in the vehicle and urea is periodically injected (A. E. El-Sharkawy, P. D. Kalantzis, M. A. Syed and D. J. Snyder, SAE International Journal of Passenger Cars-Mechanical Systems, 2 (2009) 1042).
The adsorber technology (LNT) is a technology of removing NOx by storing NOx generated under a condition (lean condition) where oxygen exists in a large amount in the exhaust gas and reducing the stored NOx under a condition (rich condition) where oxygen exists in a small amount, and has merits in that low temperature and high temperature performances are excellent and an additional infrastructure required in the urea/SCR system is not required. However, there are drawbacks in that since a large amount of noble metal catalyst is used, cost thereof is high, an engine operation is complicated, and the technology is weak to poisoning by sulfur (H. Shinjoh, N. Takahashi, K. Yokoda and N. Sugiura, Appl. Catal. B, 15 (1998) 189).
In a HC/SCR technology developed as an alternative technology of the urea/SCR technology and the LNT technology, nitrogen oxide is removed by using hydrocarbons exhausted from the exhaust gas or diesel used as fuel as the reductant. However, the HC/SCR technology has a drawback in that the low activity is exhibited at low temperatures as compared to the urea/SCR technology.
In order to increase the activity at low temperatures of the HC/SCR, study of using alcohol-based hydrocarbons and oxygenated hydrocarbons as the reductant (K. Shimizu, M. Tsuzuki, A. Satsuma, Appl. Catal. B: Environ., 71 (2007) 80), or simultaneously using diesel fuel and ethanol as the reductant has been conducted (M. K. Kim, P. S. Kim, J. H. Baik, I.-S, Nam, B. K. Cho and S. H. Oh, Appl. Catal. B, 105 (2011) 1). However, low activity is still exhibited at 250° C. or less, and thus there is a need to develop a reductant or a catalyst system exhibiting high nitrogen oxide removing efficiency even at low temperatures in order to apply the technology to a commercial system in practice.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.